Mitochondrial metabolic suppression and reactive oxygen species production during hypometabolism in mammals

During hibernation, daily torpor, and fasting, mammals reduce metabolic rate (MR) up to 99%, 95%, and 30%, respectively, compared to resting levels. Mitochondrial metabolic suppression likely contributes to this MR reduction, and the first objective of this study was to determine the relative contributions of active, regulated inhibition and passive thermal effects as body temperature (Tb) falls, to mitochondrial metabolic suppression, and to examine the mechanisms involved using top-down elasticity analysis and novel statistical approach. The second objective of this study was to determine how mitochondrial metabolic suppression affects mitochondrial reactive oxygen species (ROS) production, a topic which has been largely ignored previously. To accomplish these objectives, I measured in vitro respiration and ROS production rates of mitochondria from liver, skeletal muscle, and/or heart during hibernation in thirteen-lined ground squirrels (Ictidomys tridecemlineatus), spontaneous daily torpor and fasting in dwarf Siberian hamsters (Phodopus sungorus), and fasting-induced daily torpor and fasting in laboratory mice (Mus musculus) over a range of physiologically-relevant temperatures. In liver, state 3 respiration measured at 37°C was 70%, 35%, and 31% lower during hibernation, daily torpor, and fasting, respectively, resulting largely from substrate oxidation inhibition at complex I and/or II. In skeletal muscle, state 3 respiration measured at 37°C was reduced up to 32% during hibernation. By contrast, in heart, state 3 respiration measured at 37°C was 2-fold higher during daily torpor in hamsters. Therefore, active, regulated mitochondrial metabolic suppression in several tissues characterizes mammalian hypometabolism, accounting for up to 16% of the MR reduction observed. In all tissues, mitochondrial respiration declined with in vitro assay temperature, and differences among metabolic states were not observed at low temperatures (10-15°C), suggesting that passive thermal effects also play an important role, particularly during steady-state torpor when body temperature is low. In liver and heart (but not skeletal muscle), basal ROS production and/or free radical leak (FRL; proportion of electron flux leading to ROS production) was generally higher during hypometabolism when measured at 37°C, particularly at complex III. However, in all tissues, ROS production and FRL typically declined with temperature, suggesting that, while mitochondrial metabolic suppression may increase the potential for mitochondrial ROS production, perhaps leading to oxidative stress during fasting, low Tb during torpor may, in fact, alleviate the accumulation of oxidative damage

Inbuilt Mechanisms for Overcoming Functional Problems Inherent in Hepatic Microlobular Structure

This paper is funded by an MRC/EPSRC Discipline Bridging Initiative Grant (G0502256-77947) to W. Wan

CD161(+) Tconv and CD161(+) Treg Share a Transcriptional and Functional Phenotype despite Limited Overlap in TCR beta Repertoire

Human regulatory T cells (Treg) are important in immune regulation, but can also show plasticity in specific settings. CD161 is a lectin-like receptor and its expression identifies an effector-like Treg population. Here, we determined how CD161+ Treg relate to CD161+ conventional T cells (Tconv). Transcriptional profiling identified a shared transcriptional signature between CD161+ Tconv and CD161+ Treg, which is associated with T helper (Th)1 and Th17 cells, and tissue homing, including high expression of gut-homing receptors. Upon retinoic acid (RA) exposure, CD161+ T cells were more enriched for CCR9+ and integrin α4+β7+ cells than CD161− T cells. In addition, CD161+ Tconv and CD161+ Treg were enriched at the inflamed site in autoimmune arthritis, and both CD161+ and CD161− Treg from the inflamed site were suppressive in vitro. CD161+ T cells from the site of autoimmune arthritis showed a diminished gut-homing phenotype and blunted response to RA suggesting prior imprinting by RA in the gut or at peripheral sites rather than during synovial inflammation. TCRβ repertoires of CD161+ and CD161− Tconv and Treg from blood showed limited overlap whereas there was clear overlap between CD161+ and CD161− Tconv, and CD161+ and CD161− Treg from the inflamed site suggesting that the inflamed environment may alter CD161 levels, potentially contributing to disease pathogenesis

Clinically speaking: A communication skills program for students from non-English speaking backgrounds

This paper reports on the design, delivery and evaluation of an innovative oral communication skills program for first year students in a Bachelor of Nursing degree at an Australian university. This program was introduced in 2004 to meet the needs of first year undergraduate students from non-English speaking backgrounds who had experienced difficulties with spoken English while on clinical placement. The program consisted of early identification of students in need of communication development, a series of classes incorporated into the degree program to address students' needs, followed by a clinical placement block. This paper describes the structure of the program, discusses some of the major problems encountered by students in the clinical setting and presents some of the teaching strategies used to address these problems. Evaluations of the program suggest that students' communication skills and confidence improved, resulting in a more positive clinical experience for the majority of students

R2 imaging of ferritin iron in thalassaemia patients off and on iron-chelation therapy

Myocardial Tissue Characterization: Fat, Hemorrhage & Edema - Poster presentationAccurate assessment of iron burden is crucial for the management of iron-chelation therapy. MRI provides a means to non-invasively assess tissue iron concentration by exploiting the paramagnetic effects of iron on the relaxation rates of solvent protons. The most widely used method is R2* imaging, which has been shown to be sensitive to myocardial iron overload. Recently, a breath-hold fast spin echo sequence has been proposed for fast and accurate imaging of myocardial and hepatic R2. The purpose of this study was to determine which relaxation rates are sensitive to iron-chelation therapy.published_or_final_versionThe 17th Scientific Meeting & Exhibition of the International Society of Magnetic Resonance in Medicine (ISMRM), Honolulu, HI., 18-24 April 2009. In Proceedings of ISMRM 17th Scientific Meeting & Exhibition, 2009, p. 375

Presynaptic actions of 4-Aminopyridine and γ-aminobutyric acid on rat sympathetic ganglia in vitro

Responses to bath-applications of 4-aminopyridine (4-AP) and -aminobutyric acid (GABA) were recorded intracellularly from neurones in the rat isolated superior cervical ganglion. 4-aminopyridine (0.1–1.0 mmol/l) usually induced spontaneous action potentials and excitatory postsynaptic potentials (EPSPs), which were blocked by hexamethonium. Membrane potential was unchanged; spike duration was slightly increased. Vagus nerve B-and C-fibre potentials were prolonged. In 4-AP solution (0.1–0.3 mmol/l), GABA (0.1 mmol/l), 3-aminopropanesulphonic acid or muscimol evoked bursts of spikes and EPSPs in addition to a neuronal depolarization. These bursts, which were not elicited by glycine, glutamate, taurine or (±)-baclofen, were completely antagonised by hexamethonium, tetrodotoxin or bicuculline methochloride. It is concluded that: (a) 4-AP has a potent presynaptic action on sympathetic ganglia; (b) presynaptic actions of GABA can be recorded postsynaptically in the presence of 4-AP; and (c) the presynaptic GABA-receptors revealed in this condition are similar to those on the postsynaptic membrane

Comparative reactivity of the myeloperoxidase-derived oxidants HOCl and HOSCN with low-density lipoprotein (LDL): Implications for foam cell formation in atherosclerosis

© 2015 Elsevier Inc. All rights reserved. Abstract Atherosclerosis is characterised by the accumulation of lipids within macrophages in the artery wall. Low-density lipoprotein (LDL) is the source of this lipid, owing to the uptake of oxidised LDL by scavenger receptors. Myeloperoxidase (MPO) released by leukocytes during inflammation produces oxidants that are implicated in atherosclerosis. Modification of LDL by the MPO oxidant hypochlorous acid (HOCl), results in extensive lipid accumulation by macrophages. However, the reactivity of the other major MPO oxidant, hypothiocyanous acid (HOSCN) with LDL is poorly characterised, which is significant given that thiocyanate is the favoured substrate for MPO. In this study, we comprehensively compare the reactivity of HOCl and HOSCN with LDL, and show key differences in the profile of oxidative damage observed. HOSCN selectively modifies Cys residues on apolipoprotein B100, and oxidises cholesteryl esters resulting in formation of lipid hydroperoxides, 9-hydroxy-10,12-octadecadienoic acid (9-HODE) and F2-isoprostanes. The modification of LDL by HOSCN results macrophage lipid accumulation, though generally to a lesser extent than HOCl-modified LDL. This suggests that a change in the ratio of HOSCN:HOCl formation by MPO from variations in plasma thiocyanate levels, will influence the nature of LDL oxidation in vivo, and has implications for the progression of atherosclerosis

Integrin-mediated interactions with extracellular matrix proteins for nucleus pulposus cells of the human intervertebral disc.

The extracellular matrix (ECM) of the human intervertebral disc is rich in molecules that interact with cells through integrin-mediated attachments. Porcine nucleus pulposus (NP) cells have been shown to interact with laminin (LM) isoforms LM-111 and LM-511 through select integrins that regulate biosynthesis and cell attachment. Since human NP cells lose many phenotypic characteristics with age, attachment and interaction with the ECM may be altered. Expression of LM-binding integrins was quantified for human NP cells using flow cytometry. The cell-ECM attachment mechanism was determined by quantifying cell attachment to LM-111, LM-511, or type II collagen after functionally blocking specific integrin subunits. Human NP cells express integrins β1, α3, and α5, with over 70% of cells positive for each subunit. Blocking subunit β1 inhibited NP cell attachment to all substrates. Blocking subunits α1, α2, α3, and α5 simultaneously, but not individually, inhibits NP cell attachment to laminins. While integrin α6β1 mediated porcine NP cell attachment to LM-111, we found integrins α3, α5, and β1 instead contributed to human NP cell attachment. These findings identify integrin subunits that may mediate interactions with the ECM for human NP cells and could be used to promote cell attachment, survival, and biosynthesis in cell-based therapeutics